Automated data storage libraries are known for providing cost effective storage and retrieval of large quantities of data. The data in automated data storage libraries is typically stored on media of data storage cartridges that are, in turn, stored at storage slots or the like inside the library in a fashion that renders the media, and its resident data, accessible for physical retrieval. Such data storage cartridges are commonly termed “removable media.” Data storage cartridge media may comprise any type of media on which data may be stored and which may serve as removable media, including but not limited to magnetic media (such as magnetic tape or disks), optical media (such as optical tape or disks), electronic media (such as PROM, EEPROM, flash PROM, CompactFlash™, Smartmedia™, Memory Stick™, etc.), or other suitable media. An example of a data storage cartridge that is widely employed in automated data storage libraries for mass data storage is a magnetic tape cartridge.
In addition to data storage media, automated data storage libraries typically comprise data storage drives that store data to, and/or retrieve data from, the data storage cartridge media. Further, automated data storage libraries typically comprise I/O stations at which data storage cartridges are supplied or added to, or removed from, the library. The transport of data storage cartridges between data storage slots, data storage drives, and I/O stations is typically accomplished by one or more accessors. Such accessors have grippers for physically retrieving the selected data storage cartridges from the storage slots within the automated data storage library and transporting such cartridges to the data storage drives by moving, for example, in the X and Y directions.
In an effort to increase storage capacity, deep slot technology allows for storage cells that contain more than a single data storage cartridge. Such storage libraries allow for higher density, or more cartridges stored per square foot. In ‘deep slot’ libraries, two or more cartridges may be stored in a multi-cartridge deep slot cell, arrayed in series, one behind the other, in tiers ranging from a frontmost tier to a rearmost tier.
Placing a data storage cartridge in a multi-cartridge deep slot cell results in moving any cartridge(s) already in the cell towards the rearmost tier, thereby “demoting” those cartridge(s). When the rearmost tier is filled with a cartridge, the entire deep slot cell is full.
Accessing a desired cartridge not at the frontmost tier thus requires removing cartridges stored in front of the desired cartridge, temporarily depositing the removed cartridge(s) at some available storage, accessing the desired cartridge, and replacing the previously removed cartridge(s). As the result of removal of the accessed cartridge, the cartridges originally behind and remaining in the deep slot cell are “promoted” to positions closer to, or at the frontmost tier.
Accessing data storage cartridges from positions not at the frontmost tier tends to decrease the performance of the automated data storage library in accordance with the number of tiers of the position of the accessed cartridges from the frontmost tier.